Flight International Online news 09:00GMT: Investigators of the 14 August Helios Airways accident in Greece have discovered there have been many other cases of a Boeing 737 climbing without pressurisation set, but the crews recognised the alerts and averted crew hypoxia and resultant disaster.
At the same time, the seasonal nature of Helios’s operations and its effect on the airline’s safety culture are under the microscope, according to the head of the Hellenic Air Accident Investigation and Aviation Safety Board, Capt Akrivos Tsolakis.
Speaking to Flight International at the Flight Safety Foundation/International Air Travel Association/International Federation of Airworthiness safety seminar in Moscow last week, Tsolakis said he had received reports from numerous other national aviation authorities advising him of events similar to the Helios one, but with non-fatal outcomes. Before the flight, maintenance crew who had carried out a pressurisation check left the control in manual instead of automatic, so the aircraft did not pressurise as it climbed. But the crew failed to notice the setting in their pre-take-off checks, and the post-take-off checks require no further confirmation of the pressurisation control selection.
In the Helios case, when the audible cabin altitude alert sounded, the crew thought it was an erroneous configuration warning because the sound is identical, and their subsequent mindset and actions were determined by this preconception until hypoxia overcame them as the aircraft continued to climb, said Tsolakis. None of the crew had been exposed to the symptoms of hypoxia in a decompression chamber during any of their training, said Tsolakis. Early investigations suggest the airline had not drawn up its own codes of operating practice, he added.
Investigators are trying to determine whether the fact that Helios flew regular schedules in the summer and partly as a wet-lease operator in the winter has any bearing on the company culture. The situation appears not to have been questioned by the Cyprus civil aviation authorities.
Meanwhile, Boeing may be asked to account for why, following non-fatal precursor events, no changes were made to the 737 operations manual advice on pressurisation system management – although appropriate amendments have now been issued to operators.